Dielectric strength test as per IEC 60601-1 -Infant incubator

#1
hi
we got an infant incubator for safety testing as per IEC 60601-1. I am new to the testing field. So after reading the standard (which are a little bit difficult for me to interpret )and some old reports, I made these points on which HV test should be done.
1. between Line neutral shorted and earth​
2. between line neutral shorted and the display panel (using metal foil)​
3. between line neutral shorted and the applied part ( which is infant temperature sensor)​
4. between line neutral shorted and the metallic enclosure.​
the incubator has SMPS which is an approved component.

Please check if I am doing it right or if I missed anything.

also, while reading other threads on this topic, people are suggesting not to do HV test on an assembled device(it is a class I device), then how should I do testing?
it will be very helpful to me in understanding things.

PS: The insulation diagram given by the manufacturer is attached.
 

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#2
Sounds wrong, sorry!

Dielectric strength is a test for solid insulation. In practical form it exists in parts like capacitors, optocouplers, transformers, wiring.

Before performing the test, you should know exactly where the insulation is based on inspection. It's a good idea to make a list of all the insulating parts for each insulation barrier as a supplement to the insulation diagram. For example, in the diagram provided, insulation "a" is between mains and earth. You should be able to inspect the device and list all the physical components that make up this barrier. For an infant incubator, this is very difficult (maybe, one of the most difficult) but in fact that makes it all the more important.

If the parts are certified and used within specification, you don't actually need to do a HV test (dielectric strength). However, this is not widely understood and it is generally expected to have some tests in a report. Even so it's good to keep this in mind especially as some parts are difficult to test in the final product.

In principle, tests should be performed on the individual parts.

Even so, as a general rule the 1.5kV tests (for 230V rating) can be done on an assembled device. In truth such tests do not necessarily stress the insulation that might be identified. For example, mains wiring is often used which has a solid insulation. But, in test sample of the final product, the particular wiring may be sitting in air, and not in contact with earth metal. So, it won't get tested in an assembled device. Another example may be parts of the circuit that are not connected due to switching or relays. Personally, I don't care about these situations, it is more important (and correct) to confirm that the wiring or parts are certified than to worry about the tests in an assembled device.

As a general rule, 4kV tests can not (and should not) be done in an assembled device. There are high risks of damaging parts that are not intended to provide 4kV and it's also likely that the real insulation does not get tested. The 4kV test should only be done on the part itself, disassembled from the device, or better still waived (not done) based on component certification (e.g. certified power supply).

For an infant incubator, there are two typically problematic areas:
- the heater itself, which is usually custom made and hence has no certifications, and also contains powder insulation which needs to be sealed against moisture. You will need to study the design, do full testing including the humidity pre-conditioning.
- internal connectors and wiring which route through to the heater and lamps, make sure double insulation is provided to any unearthed parts (including secondary wiring), using for example sleeving, and connectors have appropriate spacing if the connector has mains and other parts such as earthing or secondary circuits.

Infant incubators are really tough but it just needs to be approached systematically, break it down and make a one page assessment for each area, listing the parts, certifications, spacings etc. If you can't inspect the part, ask the manufacturer for additional samples and also drawings.
 
#3
hi, I couldn't reply to you earlier due to sudden lockdown. first of all, thank you so much for explaining in so detailed manner. I hope standards are also written in such understandable language.
I just have one doubt, we got two models of the infant warmer. My superior is doing the 4 kV test on the assembled product itself saying it is as per his understanding. Point is, one model is getting passed while another is getting failed both on DC as well as AC. I couldn't convince my superior regarding not doing this 4 kV test on assembled product. What should I do?

you suggested to disassembled the part(patient connection) and perform the test on the part itself. Can you elaborate on this process? it will be a great help.
 
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